The present invention relates generally to coating compositions and specifically to a solvent soluble resin paint or varnish having water dispersed therein.
It has been a desideratum in the coatings art to formulate a paint, varnish or other protective coating composition which employs an organic solvent soluble film-forming component and which further includes water as part of the evaporative vehicle.
Presently such compositions, commonly called solvent or solution resin coatings, comprise organic solvents as the evaporative vehicle, often in amounts in excess of 60% of the total composition. As this solvent evaporates during the drying of the coating, considerable irritation and odor may be caused by the escape of these fumes in the atmosphere. Also, organic solvents are not inexpensive, and contribute substantially to the cost of the coating composition. In addition, as organic solvents are highly flammable they are hazardous during the manufacture and use of the coatings, and add to the fireload and insurance costs of manufacturing and warehouse facilities. For these reasons, it has been desirable to substitute water for part of the solvents previously employed.
Heretofore, water containing coatings have required water soluble or dispersable film-forming components, and latex paint, for example, has met with wide acceptance. Latex paint is composed of two dispersions. First, a dispersion of pigments and various extenders in water, and second, a dispersion of the resin in the water. The resin dispersion is either a latex formed by emulsion polymerization or a resin in emulsion form. Such paints are characterized by the fact that the film-forming component is in a water-dispersed form. The principle film-forming components in latex paints are styrene-butadiene, polyvinyl acetate, and acrylic resins.
However, latex coating compositions are not without their disadvantages. First, as the latex composition is a double dispersion, it requires two emulsifiers which may conflict and may, in particular, cause problems in formulation due to the fact that the emulsifier used in the polymerization of the resin may be unknown and have an unpredictable effect on the final product. In addition, the oil-in-water emulsion found in latex compositions will not dry to produce the clear or gloss finish found in solvent coatings such as varnish and the like. Oil-in-water emulsion clear coatings, due to the latex resins used, tend to form with brush marks or surface disruptions and cannot be easily sanded or otherwise refinished as can traditional solvent varnishes.
Also, latex coatings are not easily adaptable to use in pressurized cans commonly referred to as aerosol containers. This is due to the high viscosity of the latex composition and the tendency of the latex oil-in-water emulsion to foam excessively when sprayed from an aerosol container. This foaming begins, as the composition leaves the nozzle and becomes apparent after the coating has been applied to the substrate or workpiece. For example, previous water base spray paints dry with small craters rather than a smooth surface which indicates that foaming has occurred during the application process. Thus, when the foam dries there is left a penetrable film which seriously affects the protective value of the coating. In addition, as the propellant must be miscible in the continuous phase in order to properly atomize the emulsion for spraying, suitable i.e. water soluble propellants have led to an excessive product cost and have been otherwise unsatisfactory.